Compacting machine having variable vibration

ABSTRACT

A rotatably driven eccentric carrier has its axis parallel to that of a compacting machine drum. A large eccentric mass fixed to one side of the carrier is only partially counterbalanced by a smaller radially movable mass thereon; hence centrifugally responsive movement of the smaller mass decreases vibration amplitude. The radial position of the smaller mass is controlled by a single-acting hydraulic jack on the carrier, connected with an accumulator through a manually operable valve. Speed of carrier rotation is controllable. A pressure responsive cutout switch in the jack-accumulator circuit prevents overspeed.

United States Patent 1191 Barrett et a1.

1 1 June 4,1974

[ COMPACTING MACHINE HAVING VARIABLE VIBRATION [75] Inventors: John C. Barrett; Roger L. Larson,

both of Minneapolis, Minn.

[30] Foreign Application Priority Data 3.656.419 4/1972 Boone 404/1 17 3.722.381 3/1973 Tuneblom 404/117 FOREIGN PATENTS OR APPLlCATlONS 1.359.854 3/1964 France 404/1 17 766.593 1/1957 Great Britain 74/61 769.547 3/1957 Great Britain 74/61 Primary E.\'aminerR0y D. Frazier Assistant ExuminerThomas .1. Holko 1571 ABSTRACT A rotatably driven eccentric carrier has its axis parallel to that of a compacting machine drum. A large eccentric mass fixed to one side of the carrier is only partially counterbalanced by a smaller radially movable mass thereon; hence centrifugally responsive movement of the smaller mass decreases vibration amplitude. The radial position of the smaller mass is controlled by a single-acting hydraulic jack on the carrier. connected with an accumulator through a manually operable valve. Speed of carrier rotation is controllable. A pressure responsive cutout switch in the jackaccumulator circuit prevents overspeed.

5 Claims, 6 Drawing Figures FATENTEUJUH 4 I974 SHEEI 1 [IF 4 PATENTEDJUH 4.914 3514.532

SHEET OF 4 SPEED SENSOR SPEED SELECTOR AN D DIRECTION CONTROL 4 WAY VALVE COMPACTING MACHINE HAVING VARIABLE VIBRATION This invention relates to machines for compacting freshly laid asphalt paving, soil, and similar materials; and the invention more particularly concerns a compacting machine in which the desired compaction is produced not only by traverse of a heavy drum or roller over the surface of the material but also by imparting vibration to the drum.

A compacting machine of the type with which the present invention is concerned is usually self propelled. It comprises at least one surface engaging roller or drum and in most cases a pair of traction wheels. When wheels provide the driving traction, the drum is usually freely rotatable, but in some machines there is a second drum in place of the wheels, and one or both of the drums may be rotatably driven. For purposes of example, the invention will be herein described with reference to a machine having a freely rotatable drum and a pair of traction wheels.

In the machine of the present invention, as in prior machines of this type, vibration of the drum is produced by eccentric mass means revolving rapidly about an axis parallel to that of the drum as the drum rolls slowly over the surface of material being compacted. Such vibration of the drum is known to improve the ability of the machine to effect a complete and rapid compaction. It is also known that the amplitude of the vibration greatly affects the character of work accomplished by such a machine. High amplitude vibration quickly produces desired densities in the material being compacted but may leave its surface ridged or rough, while low amplitude vibration makes possible the production of exceptionally smooth surfaces. In prior machines, however, the amplitude of vibration was fixed, so that the machine was best suited either for preliminary compaction or for finish work, oras was most often the casethe machine was designed for a compromise vibration amplitude that did not do either type of work completely satisfactorily, in the interests of doing both reasonably well.

By contrast, it is an object of the present invention to provide a machine of the character described that accomplishes both preliminary and finish compaction with the utmost efficiency by reason of the fact that it can selectively produce either high or low amplitude vibration.

It is also an object of this invention to provide a machine of the character described which has simple, inexpensive and efficient means for effecting changes in vibration amplitude under the control of an operator, wherein centrifugal force of an eccentric vibration producing mass is utilized in accomplishing such change in vibration amplitude when the vibration producing apparatus is in operation.

Another object of the invention is to provide a compacting machine in which the operator can cause the machine to operate with a high vibration amplitude during preliminary compacting, and then, as the job nears completion, can manually shift to low amplitude vibration without having to stop the machine or the vibration producing apparatus in order to do so, but which machine fails safe in that it cannot be shifted during operation, nor shift itself, from low amplitude to high amplitude vibration, thus avoiding any possibility of ruining a nearly complete, smoothly finished compacted surface.

A further object of this invention is to provide a compacting machine wherein the frequency as well as the amplitude of vibration can be controlled by the operator, so that he can readily adapt the machine to different surface compacting requirements, and wherein means are provided that cooperate with the vibration amplitude control apparatus to prevent overspeeding of the vibration producing means.

In general the objects of the invention are achieved by providing a carrier which is driven for rotation about an eccentric axis that is parallel to the drum axis and preferably coincides with the drum axis, and an eccentric mass which is so mounted on the carrier as to be constrained to rotate therewith but to be movable radially toward and from the eccentric axis between defined limits. Centrifugally propelled outward motion of thismovable mass is opposed by a releasable locking device, such as a hydraulic jack, which can also be mounted on the carrier for rotation therewith. By closure of a manually controlled valve connected with the jack, fluid can be prevented from escaping therefrom, thus confining the movable mass against Centrifugally responsive outward motion. The movable mass is overbalanced by a second, diametrically opposite eccentric mass which is fixed to the carrier and which has a moment larger than the greatest moment exerted by the movable mass; hence vibration amplitude can be decreased merely by opening the valve to permit the movable mass to move outward in response to centrifugal force. A pressure responsive cutout switch in the hydraulic circuit for the jack prevents overspeeding of the vibration producing means.

With these observations an objectives in mind, the manner in which the invention achieves its purpose will be appreciated from the following description and the accompanying drawings which exemplify the invention, it being understood that changes may be made in the specific apparatus disclosed herein without departing from the essentials of the invention set forth in the appended claims.

The accompanying drawings illustrate one complete example of an embodiment of the invention constructed according to the best mode so far devised for the practical application of the principles thereof, and in which:

FIG. 1 is a front perspective view of a compacting machine embodying the principles of the present invention;

FIG. 2 is a view generally in longitudinal section through the drum of the compacting machine illustrated in FIG. 1;

FIG. 3 is a fragmentary sectional view on a larger scale, taken on the plane of the line 3-3 in FIG. 2 and showing the vibration producing means in its condition for producing vibration of high amplitude;

FIG. 4 is a view generally similar to FIG. 3, but with portions of the pressure responsive means shown broken away and illustrating the vibration producing means in its low amplitude condition;

FIG. 5 is a schematic diagram of the electrohydraulic control system in the machine of this invention whereby the operator of the machine is enabled to control both the amplitude and the frequency of vibration; and

I of the machine. The machine is steerable as it moves over material to be compacted by reason of the fact that the drum assembly and the tractor are articulately connected for relative motion about an upright axis. A steering wheel 8 that is conveniently accessible to the operator of the machine controls the mechanism by which steering is effected. Details of the steering mechanism and of the reversible propulsion system, being conventional and well known, are not shown.

As is also conventional, the drum assembly of the machine comprises a rigid yoke the arms 9 of which embrace the drum and have bearing mounting plates 10 connected thereto by elastic shock mounts 11 (see FIG. 2). The bearing mounting plates 10 are adjacent to the ends of the drum and carry the outer races of bearings 12 by which the drum is freely rotatably connected with the mounting plates, and through the shock mounts 11, with the arms 9 of the yoke. Vibration of the drum is therefore not imparted to the rest of the machine.

The drum is hollow, and in this case the vibration producing means, designated generally by 13, is housed within the drum and rotates about an eccentric axis which coincides with the axis of the drum, As the description proceeds it will be apparent that the invention is also applicable in principle to a machine of the type disclosed in U.S. Pat. No. 3,543,656, wherein the chas sis comprises two drums, at least one of which is power driven, and wherein the axes of the vibration producing means are above the drums and parallel to their axes.

In the machine here illustrated the innerrace of each drum bearing 12 is mounted on a hub portion of the axially outer wall 14 of a concentric housing .unit designated generally by l5. There are two such housing units 15, one fixed to each of the end walls 16,0f the drum, and each-housing unit encloses one ofthe vibration producing means 13 of this invention. Each of these housing units also has an inner wall 18, spaced axially inwardly from its outer wall 14. The walls 14 and 18 of each housing unit carry the outer races of bearings 19 by which an eccentric carriershaft 20 is journaled for rotation on an axis coinciding with that of the drum. Each shaft 20 carries eccentric masses that are described hereinafter. so that as it rotates vibration is imparted to the drum. I

Secured to one of the bearing carrying plates 10 is a hydraulic drive motor 22 that is connected'with one of the eccentric carrier shafts 20. Rotation is transmitted to the other shaft 20 by means of a concentric torque tube 23 that couples the shafts.

Referring now to FIGS. 3 and 4, the eccentric masses by which rotation of the shafts 20 is translated into vibration of the drum comprise a pair of eccentric mass elements carried by each carrier shaft 20. One of these mass elements, designated by 25, is fixed to the shaft at one side thereof and produces a substantially large eccentric moment; the other mass element 26 is constrained to rotate with the carrier shaft at the side thereof remote from the fixed mass element 25, but is so mounted as to be movable radially relative to the shaft between a high amplitude position in which it is near the eccentric axis (which position is illustrated in FIG. 3) aNd a low amplitude position (FIG. 4) in which it is at the defined outer limit of its radial relative motion. Even when the movable mass element 26 is at the outer limit of its motion, its eccentric moment is less than that of the fixed mass element 25, which is to say that the fixed mass element always overbalances the movable mass element 26. Consequentlycentrifugally responsive outward motion of the movable mass element 26 brings the moments exerted by the two mass elements more nearly into balance, decreasing the amplitude of the vibration produced by the apparatus.

In the specific embodiment here shown, the fixed mass element is generally U-shaped, with its bight portion formed as a hub 27 that closely embraces and is non-rotatably secured to the shaft 20, as by weldments 28. The massive legs 29 of the U are disposed at equal distances to opposite sides of a plane that contains the eccentric axis, and they of course project to one side of the shaft to produce the larger eccentric moment. Projecting from the bight portion of the larger mass element, in the direction opposite to its legs, are a pair of parallel guide posts 30 upon which the smaller mass element 26 is slidable for its motion relativeto the shaft. In its radially inner position the smaller mass element lies closely adjacent to the bight portion of the fixed mass element. The radially outermost position of the smaller mass element is defined by enlarged heads 31 on the outer ends of the guide posts 30.

When the vibration producing means is in operation, centrifugally responsive outward movement of the smaller mass element 26 can be prevented, to maintain high vibration amplitude, by means of readily releasable locking means, here shown as a fluid pressure responsive device 32 that comprises a single acting hydraulic jack. The cylinder 33 of the'hydraulic locking means is mounted between the legs 29 of the fixed mass element, while the rod 34 of its piston 35- slidably extends through a hole 35' in theshaft 20, (FIG. 6) parallel to and between the guide posts 30.- The outer end portion of the piston rod is secured,--as by a nut 36, to the movable mass element, through which it also ex.-

tends.

A hydraulic system that includes the rod end of each cylinder 33 also comprises, as illustrated in FIG. 5,'a yieldable fluid pressure source in the form of an accumulator 37 and a control valve 38. Essentially, the hydraulic system is a closed duct with the seriesconnected cylinders 33 at one end thereof, the accumulator 37 at its other end, and the valve 38 arranged to control flow of fluid between the cylinders and the accumulator. The control valve may be directly manually operable, but preferably is a conventional normally open solenoid actuated valve remotely operated by an amplitude selector switch located on the operators control panel (not shown).

When the valve 38 is closed, fluid is of course locked into the rod end of each cylinder, and if the movable mass elements are in their high amplitude positions, they will thus be confined against centrifugally responsive outward movement. When the amplitude selector switch is in its high amplitude position, the solenoid controlling the valve 38 is energized and the valve is closed. Conversely, when the amplitude selector switch is in its low amplitude" position, the solenoid is deenergized and the valve is open. It follows, therefore, that the only time the valve is not open is when the amplitude selector switch is in its high amplitude" position. When the vibration device is in operation and the valve 38 is open, centrifugal force on the movable mass elements 26 causes fluid to be forced out of the cylinders and into the accumulator 37. Air pressure in the accumulator, although substantially high, is not high enough to prevent such centrifugally responsive motion. Note that any failure of the hydraulic system or error in manipulation of the valve 38 can only result in low amplitude vibration.

As indicated by FIG. 5, the hydraulic system for the vibration device can also include a pressure gage 39 and a manually operable fill valve 40. The pressure gage can be removably connected to the fluid inlet port of the fill valve.

The accumulator 37 and the amplitude control valve 38 are of course mounted on relatively fixed parts of the machine. whereas the cylinders 33 rotate with the eccentric carrier shaft. Therefore the fluid passage connecting the cylinders with the relatively fixed units is in part defined by portions of each carrier shaft and also comprises a rotation accommodating union 42. Each shaft has two axial bores 43 which define the fluid passage portions therein and which open to the outer ends of the shaft but terminate short of its medial portion through which the rod of the hydraulic jack passes. The inner end of each bore 43 is connected with the rod end of its adjacent cylinder 33 by means of a conduit 44, so that the two bores in each shaft are connected through the cylinder. The mouths of the bores at the axially inner ends of the shafts are communicated with one another through a suitable high pressure conduit or hose 45 inside the torque tube 23. The rotation accommodating union 42 is at the end of the drum that is opposite the hydraulic motor 22, with its stationary component on the adjacent bearing carrying plate 10, and it of course provides for communication between its adjacent shaft bore 43 and a duct 46 that isconnected with the valve 38.

The hydraulic drive motor 22 has its stator mounted on the adjacent bearing carrying plate 10. The driving connection between its rotor and the adjacent eccenv tric carrier shaft 20 comprises a cross pin 47 that extends through a reduced diameter end portion 49 of that shaft. The adjacent axial bore 43 in the shaft is off-center but parallel to the shaft axis, opening to the shoulder defined by the reduced diameter shaft end portion 49, and the outer end of that bore 43' is closed by a bleed plug 50 that can be removed to vent air from the hydraulic system when it is being charged with fluid.

Referring back to H0. 5, the hydraulic motor 22 is supplied with pressure fluid from a pump 52 under the control of the operator. For sake of simplicity, the control system by which the operator regulates the operation of the hydraulic motor has been illustrated as comprising a solenoid actuated four-way valve 53. The spool of the valve 53'is self centering and unless shifted occupies a neutral position at which the pump is disconnected from the motor. The spool is solenoid actuatable to a pair of operating positions in which it provides for selected rotation of the motor in one direction or the other. Those skilled in the art will recognize that in lieu of the motor control system illustrated. a known form of closed loop arrangement may be used, wherein the motor and a swash plate type pump are connected to form a closed loop, and a servo valve controls the swash plate angle of the pump. the servo valve being actuated by a reversible torque motor under control of the operator.

Preferably the direction of rotation of the motor 22 is coordinated with the direction of traverse of the machine, so that the horizontal components of force due to the vibratory means will not oppose motion of the machine. Hence there can be a single instrumentality by which the operator can control both the direction in which the traction wheels are driven and the direction of rotation of the motor 22.

The operator can also have manual means for establishing a desired frequency of vibration, which frequency is of course equal to the rotational speed of the motor 22 and can be controlled by adjustments of the four-way valve 53 (or the servo valve of the closed loop system if it is used instead of the arrangement illus trated) to move it partway towards or away from one of its fully open operating positions. For the purpose of such frequency control a speed sensor 54 is mounted on the subframe side wall 10 at the side of the drum remote from the hydraulic motor 22, cooperating with a sprocket-like pulse generating device 55 that is secured to the adjacent eccentric carrier shaft 20 to rotate therewith. The speed sensor 54 is essentially a tachometer in which electrical pulses are generated at a rate dependent upon the speed of shaft rotation. Those skilled in the art will recognize that the operators vibration frequency control adjusts the rate at which pulses are generated by apparatus that produces a reference pulse train, and that the four-way valve solenoids are energized in accordance with outputs based upon a comparison of the reference pulse train with the pulses generated by the tachometer. The apparatus for generating the reference pulse train, for effecting such .comparison and for .producing such output are all known.

If by any chance the vibration frequency control apparatus should fail, the machine of the present invention has means for preventing an excessively high frequency of vibration, comprising a normally closed pressure responsive switch 56 that is hydraulically connected in the amplitude control circuit comprising the single-acting jacks 32 and the accumulator 37. It will be evident that with increasing speed of the hydraulic motor 22 centrifugal force upon the movable mass elements 26 will cause increasing pressure upon the fluid in the amplitude control hydraulic system. The pressure responsive switch 56 is set to open when pressure in its hydraulic system exceeds a critical value, which critical value somewhat exceeds the highest vibration frequency for which the apparatus is adjustable. Such opening of the pressure responsive switch interrupts the energizing circuit for the solenoids of the four-way valve, permitting the spool of that valve to center itself, thereby preventing fluid from flowing to the motor 22 from the pump 52. The pressure responsive switch 56 thus provides an over-speed safety device for the vibration producing means.

From the foregoing description taken with the accompanying drawings it will be apparent that this invention provides vibration producing means in a compacting machine of the character described wherein both the amplitude and the frequency of vibration can.

be selected by the operator of the machine. It will also be apparent that the amplitude control apparatus can any failure thereof or misuse of the amplitude control will result in low amplitude vibration.

Those skilled in the art will appreciate thatthe invention can be embodied in forms other than as herein disclosed for purposes of illustration.

The invention is defined by the following claims:

1. A machine for compacting soil and the like, said machine having a drum that rotates about its axis in rolling over the surface of material to be compacted, a member driven for rotation about an axis parallel to that of the drum, eccentric mass means carried by said member, and means operatively connecting said member with the drum to impart thereto surface compacting vibration produced by rotation of the eccentric mass means, said machine being characterized by:

A. motor means for rotatably driving said member;

B. control means for said motor by which'its speed and direction of rotation may be selected and controlled;

C. means mounting the eccentric mass means on said member for motion relative to the member toward and from the axis about which said member rotates but constraining the mass means to rotate with said member;

D. fluid pressure means so connected with said eccentric mass means as to opposte centrifugally responsive motion thereof relative to said member and in which pressure of fluid is increased by increased centrifugal force upon the eccentric mass means; and

E. overspeed preventing means comprising a pressure responsive element connected with said fluid pressure means to be responsive to fluid pressure therein and operatively connected with said control means to interrupt operation of the motor when pressure of fluid in the fluid pressure means exceeds a predetermined value.

2. A variable amplitude vibration producing device for soil compaction and the like, comprising:

A. first and second mass elements;

B. means mounting said mass elements for rotation in counterbalancing relation about an axis, with-the first mass element fixed with respect to said axis and the second mass element movable towards and from said axis between defined inner and outer lim- Its. so that the amplitude of vibration resulting from rotation of said mass elements depends upon the location of said second mass element with re- 8 spect to said axis;

C. hydraulic cylinder and piston means connecting said mass elements with the cylinder fixed with respect to one mass element and the piston fixed with respect to the other mass element, so that the mass elements can not move relative to one another without corresponding relative movement between the piston and cylinder;

D. a yieldable fluid pressure source I E. a closed hydraulic circuit having connected therein the yieldable fluid pressure source and the space in the cylinder at the side of the piston that faces the mass element with respect to which the piston is fixed;

F. hydraulic fluid in said closed circuit filling said space in the cylinder and manifesting in said space the pressure of said yieldable fluid pressure source, the yieldable fluid pressure sourcemaintaining the hydraulic fluid under a pressure that is sufficient to hold the movable second mass element at its inner limit of movement when the mass elements are not rotating, but insufficient when the mass elements are rotating above a predetermined speed, to prevent displacement of hydraulic fluid from the cylinder and consequent movement of the movable second mass element towards its outer limit of movement in response to centrifugal force acting thereon; and

G. control valve means in'said closed hydraulic circuit between the cylinder and the yieldable fluid pressure source operable to either prevent or permit hydraulic fluid to be displaced from the cylinder.

3. The invention of claim 2, further characterized in that said first mass element has a moment greater than the largest moment that can be exerted by the second mass element.

4. The invention of claim 2, wherein said yieldable fluid pressure source is a pressure accumulator.

5. The machine of claim 2, further characterized by:

exceeds a predetermined value. 

1. A machine for compacting soil and the like, said machine having a drum that rotates about its axis in rolling over the surface of material to be compacted, a member driven for rotation about an axis parallel to that of the drum, eccentric mass means carried by said member, and means operatively connecting said member with the drum to impart thereto surface compacting vibration produced by rotation of the eccentric mass means, said machine being characterized by: A. motor means for rotatably driving said member; B. control means for said motor by which its speed and direction of rotation may be selected and controlled; C. means mounting the eccentric mass means on said member for motion relative to the member toward and from the axis about which said member rotates but constraining the mass means to rotate with said member; D. fluid pressure means so connected with said eccentric mass means as to opposte centrifugally responsive motion thereof relative to said member and in which pressure of fluid is increased by increased centrifugal force upon the eccentric mass means; and E. overspeed preventing means comprising a pressure responsive element connected with said fluid pressure means to be responsive to fluid pressure therein and operatively connected with said control means to interrupt operation of the motor when pressure of fluid in the fluid pressure means exceeds a predetermined value.
 2. A variable amplitude vibration producing device for soil compaction and the like, comprising: A. first and second mass elements; B. means mounting said mass elements for rotation in counterbalancing relation about an axis, with the first mass element fixed with respect to said axis and the second mass element movable towards and from said axis between defined inner and outer limits, so that the amplitude of vibration resulting from rotation of said mass elements depends upon the location of said second mass element with respect to said axis; C. hydraulic cylinder and piston means connecting said mass elements with the cylinder fixed with respect to one mass element and the piston fixed with respect to the other mass element, so that the mass elements can not move relative to one another without corresponding relative movement between the piston and cylinder; D. a yieldable fluid pressure source E. a closed hydraulic circuit having connected therein the yieldable fluid pressure source and the space in the cylinder at the side of the piston that faces the mass element with respect to which the piston is fixed; F. hydraulic fluid in said closed circuit filling said space in the cylinder and manifesting in said space the pressure of said yieldable fluid pressure source, the yieldable fluid pressure source maintaining the hydraulic fluid under a pressure that is sufficient to hold the movable second mass element at its inner limit of movement when the mass elements are not rotating, but insufficient when the mass elements are rotating above a predetermined speed, to prevent displacement of hydraulic fluid from the cylinder and consequent movement of the movable second mass element towards its outer limit of movement in response to centrifugal force acting thereon; and G. control valve means in said closed hydraulic circuit between the cylinder and the yieldable fluid pressure source operable to either prevent or permit hydraulic fluid to be displaced from the cylinder.
 3. The invention of claim 2, further characterized in that said first mass element has a moment greater than the largest moment that can be exerted by the second mass element.
 4. The invention of claim 2, wherein said yieldable fluid pressure source is a pressure accumulator.
 5. The machine of claim 2, further characterized by: F. a motor by which said mass elements are rotatably driven; G. control means for said motor by which its speed and direction of rotation may be controlled; and H. overspeed preventing means comprising a pressure responsive element connected with said cylinder to respond to fluid pressure therein that is produced by centrifugal force acting on the first mass element and having an operative connection with said control means by which operation of the motor is interrupted when such centrifugal force exceeds a predetermined value. 